Electronic systems in use today perform a remarkably broad range of functions, but they share the technical characteristic of employing electron devices such as vacuum tubes, transistors, or integrated circuits. Most electron devices in use today function as electric switches or valves, controlling a flow of electrons in order to perform useful tasks. Electron devices differ from ordinary electromechanical switches or current- or voltagecontrol devices in that an applied electric current or field controls electron flow rather than a mechanical device. Electronic devices are ‘‘active,’’ like machines, but have no moving parts, so engineers distinguish them both from electromechanical devices and from other ‘‘passive’’ electrical components such as wires, capacitors, transformers, and resistors. When the word electronics was coined around 1930, it usually referred to so-called vacuum tubes (valves), which utilize electrons flowing through a vacuum. With the advent of the transistor in the late 1940s, a second term emerged to describe this new category of ‘‘solidstate’’ electron devices, which performed some of the same functions as vacuum tubes but consisted of solid blocks of metal.
Few of the basic tasks that electronic Technologies perform, such as communication, computation, amplification, or automatic control, are unique to electronics. Most were anticipated by the designers of mechanical or electromechanical technologies in earlier years. What distinguishes electronic communication, computation, and control is often linked to the instantaneous action of the devices, the delicacy of their actions compared to mechanical systems, their high reliability, or their tiny size.
The electronics systems introduced between the late nineteenth century and the end of the twentieth century can be roughly divided into the applications related to communications (including telegraphy, telephony, broadcasting, and remote detection) and the more recently developed fields involving digital information and computation. In recent years these two fields have tended to converge, but it is still useful to consider them separately for a discussion of their history. The origins of electronics as distinguished from other electrical technologies can be traced to 1880 and the work of Thomas Edison. While investigating the phenomenon of the blackening of the inside surface of electric light bulbs, Edison built an experimental bulb that included a third, unused wire in addition to the two wires supporting the filament. When the lamp was operating, Edison detected a flow of electricity from the filament to the third wire, through the evacuated space in the bulb. He was unable to explain the phenomenon, and although he thought it would be useful in telegraphy, he failed to commercialize it. It went unexplained for about 20 years, until the advent of wireless telegraphic transmission by radio waves. John Ambrose Fleming, an experimenter in radio, not only explained the Edison effect but used it to detect radio waves. Fleming’s ‘‘valve’’ as he called it, acted like a one-way valve for electric waves, and could be used in a circuit to convert radio waves to electric pulses so that that incoming Morse code signals could be heard through a sounder or earphone.
As in the case of the Fleming valve, many early electronic devices were used first in the field of communications, mainly to enhance existing forms of technology. Initially, for example, telephony (1870s) and radio (1890s) were accomplished using ordinary electrical and electromechanical circuits, but eventually both were transformed through the use of electronic devices. Many inventors in the late nineteenth century sought a functional telephone ‘‘relay’’; that is, something to refresh a degraded telephone signal to allow long distance telephony. Several people simultaneously recognized the possibility of developing a relay based on the Fleming valve. The American inventor Lee de Forest was one of the first to announce an electronic amplifier using a modified Fleming valve, which he called the Audion. While he initially saw it as a detector and amplifier of radio waves, its successful commercialization occurred first in the telephone industry.
The sound quality and long-distance capability of telephony was enhanced and extended after the introduction of the first electronic amplifier circuits in 1907. In the U.S., where vast geographic distances separated the population, the American Telephone and Telegraph Company (AT&T) introduced improved vacuum tube amplifiers in 1913, which were later used to establish the first coast-tocoast telephone service in 1915 (an overland distance of nearly 5000 kilometers).
These vacuum tubes soon saw many other uses, such as a public-address systems constructed as early as 1920, and radio transmitters and receivers. The convergence of telephony and radio in the form of voice broadcasting was technically possible before the advent of electronics, but its application was greatly enhanced through the use of electronics both in the radio transmitter and in the receiver. World War I saw the applications of electronics diversify somewhat to include military applications. Mostly, these were modifications of existing telegraph, telephone, and radio systems, but applications such as ground-to-air radio telephony were novel. The pressing need for large numbers of electronic components, especially vacuum tubes suitable for military use, stimulated changes in their design and manufacture and contributed to improving quality and falling prices. After the war, the expanded capacity of the vacuum tube industry contributed to a boom in low-cost consumer radio receivers. Yet because of the withdrawal of the military stimulus and the onset of the Great Depression, the pace of change slowed in the 1930s. One notable exception was in the field of television. Radio broadcasting became such a phenomenal commercial success that engineers and businessmen were envisioning how ‘‘pictures with sound’’ would replace ordinary broadcasting, even in the early 1930s. Germany, Great Britain, and the U.S. all had rudimentary television systems in place by 1939, although World War II would bring nearly a complete halt to these early TV broadcasts.
World War II saw another period of rapid change, this one much more dramatic than that of World War I. Not only were radio communications systems again greatly improved, but for the first time the field of electronics engineering came to encompass much more than communication. While it was the atomic bomb that is most commonly cited as the major technological outcome of World War II, radar should probably be called the weapon that won the war. To describe radar as a weapon is somewhat inaccurate, but there is no doubt that it had profound effects upon the way that naval, aerial, and ground combat was conducted. Using radio waves as a sort of searchlight, radar could act as an artificial eye capable of seeing through clouds or fog, over the horizon, or in the dark. Furthermore, it substituted for existing methods of calculating the distance and speed of targets. Radar’s success hinged on the development of new electronic components, particularly new kinds of vacuum tubes such as the klystron and magnetron, which were oriented toward the generation of microwaves. Subsidized by military agencies on both sides of the Atlantic (as well as Japan) during World War II, radar sets were eventually installed in aircraft and ships, used in ground stations, and even built into artillery shells. The remarkable engineering effort that was launched to make radar systems smaller, more energy efficient, and more reliable would mark the beginning of an international research program in electronics miniaturization that continues today.
Radar technology also had many unexpected applications elsewhere, such as the use of microwave beams as a substitute for long-distance telephone cables. Microwave communication is also used extensively today for satellite-to-earth communication.
The second major outcome of electronics research during World War II was the effort to build an electronic computer. Mechanical adders and calculators were widely used in science, business, and government by the early twentieth century, and had reached an advanced state of design. Yet the problems peculiar to wartime, especially the rapid calculation of mountains of ballistics data, drove engineers to look for ways to speed up the machines. At the same time, some sought a calculator that could be reprogrammed as computational needs changed. While computers played a role in the war, it was not until the postwar period that they came into their own. In addition, computer research during World War II contributed little to the development of vacuum tubes, although in later years computer research would drive certain areas of semiconductor electron device research.
While the forces of the free market are not to be discounted, the role of the military in electronics development during World War II was of paramount importance. More-or-less continuous military support for research in electronic devices and systems persisted during the second half of the twentieth century too, and many more new technologies emerged from this effort. The sustained effort to develop more compact, rugged devices such as those demanded by military systems would converge with computer development during the 1950s, especially after the invention of the transistor in late 1947. The transistor was not a product of the war, and in fact its development started in the 1930s and was delayed by the war effort. A transistor is simply a very small substitute for a vacuum tube, but beyond that it is an almost entirely new sort of device. At the time of its invention, its energy efficiency, reliability, and diminutive size suggested new possibilities for electronic systems. The most famous of these possibilities was related to computers and systems derived from or related to computers, such as robotics or industrial automation. The impetus for the transistor was a desire within the telephone industry to create an energyefficient, reliable substitute for the vacuum tube. Once introduced, the military pressed hard to accelerate its development, as the need emerged for improved electronic navigational devices for aircraft and missiles.
There were many unanticipated results of the substitution of transistors for vacuum tubes. Because they were so energy efficient, transistors made it much more practical to design battery powered systems. The small transistor radio (known in some countries simply as ‘‘the transistor’’), introduced in the 1950s, is credited with helping to popularize rock and roll music. It is also worth noting that many developing countries could not easily provide broadcasting services until the diffusion of battery operated transistor receivers because of the lack of central station electric power. The use of the transistor also allowed designers to enhance existing automotive radios and tape players, contributing eventually to a greatly expanded culture of in-car listening. There were other important outcomes as well; transistor manufacture provided access to the global electronics market for Asian radio manufacturers, who improved manufacturing methods to undercut their U.S. competitors during the 1950s and 1960s. Further, the transistor’s high reliability nearly eliminated the profession of television and radio repair, which had supported tens of thousands of technicians in the U.S. alone before about 1980.
However, for all its remarkable features, the transistor also had its limitations; while it was an essential part of nearly every cutting-edge technology of the postwar period, it was easily outperformed by the older technology of vacuum tubes in some areas. The high-power microwave transmitting devices in communications satellites and spacecraft, for example, nearly all relied on special vacuum tubes through the end of the twentieth century, because of the physical limitations of semiconductor devices. For the most part, however, the transistor made the vacuum tube obsolete by about 1960.
The attention paid to the transistor in the 1950s and 1960s made the phrase ‘‘solid-state’’ familiar to the general public, and the new device spawned many new companies. However, its overall impact pales in comparison to its successor—the integrated circuit. Integrated circuits emerged in the late 1950s, were immediately adopted by the military for small computer and communications systems, and were then used in civilian computers and related applications from the 1960s. Integrated circuits consist of multiple transistors fabricated simultaneously from layers of semiconductor and other materials. The transistors, interconnecting ‘‘wires,’’ and many of the necessary circuit elements such as capacitors and resistors are fabricated on the ‘‘chip.’’ Such a circuit eliminates much of the laborious process of assembling an electronic system such as a computer by hand, and results in a much smaller product. The ability to miniaturize components through integrated circuit fabrication techniques would lead to circuits so vanishingly small that it became difficult to connect them to the systems of which they were a part. The plastic housings or ‘‘packages’’ containing today’s microprocessor chips measure just a few centimeters on a side, and yet the actual circuits inside are much smaller. Some of the most complex chips made today contain many millions of transistors, plus millions more solid-state resistors and other passive components.
While used extensively in military and aerospace applications, the integrated circuit became famous as a component in computer systems. The logic and memory circuits of digital computers, which have been the focus of much research, consist mainly of switching devices. Computers were first constructed in the 1930s with electromechanical relays as switching devices, then with vacuum tubes, transistors, and finally integrated circuits. Most early computers used off-the-shelf tubes and transistors, but with the advent of the integrated circuit, designers began to call for components designed especially for computers. It was clear to engineers at the time that all the circuits necessary to build a computer could be placed on one chip (or a small set of chips), and in fact, the desire to create a ‘‘computer on a chip’’ led to the microprocessor, introduced around 1970. The commercial impetus underlying later generations of computer chip design was not simply miniaturization (although there are important exceptions) or energy efficiency, but also the speed of operation, reliability, and lower cost. However the inherent energy efficiency and small size of the resulting systems did enable the construction of smaller computers, and the incorporation of programmable controllers (special purpose computers) into a wide variety of other technologies. The recent merging of the computer (or computer-like systems) with so many other technologies makes it difficult to summarize the current status of digital electronic systems. As the twentieth century drew to a close, computer chips were widely in use in communications and entertainment devices, in industrial robots, in automobiles, in household appliances, in telephone calling cards, in traffic signals, and in a myriad other places. The rapid evolution of the computer during the last 50 years of the twentieth century was reflected by the earmeaninglessness of its name, which no longer adequately described its functions. From an engineering perspective, not only did electronics begin to inhabit, in an almost symbiotic fashion, other technological systems after about 1950, but these electronics systems were increasingly dominated by the use of semiconductor technology. After virtually supplanting the vacuum tube in the 1950s, the semiconductor-based transistor became the technology of choice for most subsequent electronics development projects. Yet semiconducting alloys and compounds proved remarkably versatile in applications at first unrelated to transistors and chips. The laser, for example, was originally operated in a large vacuum chamber and depended on ionized gas for its operation. By the 1960s, laser research was focused on the remarkable ability of certain semiconducting materials to accomplish the same task as the ion chamber version. Today semiconductor devices are used not only as the basis of amplifiers and switches, but also for sensing light, heat, and pressure, for emitting light (as in lasers or video displays), for generating electricity (as in solar cells), and even for mechanical motion (as in micromechanical systems or MEMS). However, semiconductor devices in ‘‘discrete’’ forms such as transistors, would probably not have had the remarkable impact of the integrated circuit. By the 1970s, when the manufacturing techniques for integrated circuits allowed high volume production, low cost, tiny size, relatively small energy needs, and enormous complexity; electronics entered a new phase of its history, having a chief characteristic of allowing electronic systems to be retrofitted into existing technologies. Low-cost microprocessors, for example, which were available from the late 1970s onward, were used to sense data from their environment, measure it, and use it to control various technological systems from coffee machines to video tape recorders. Even the human body is increasingly invaded by electronics; at the end of the twentieth century, several researchers announced the first microchips for implantation directly in the body. They were to be used to store information for retrieval by external sensors or to help deliver subcutaneous drugs. The integrated circuit has thus become part of innumerable technological and biological systems.
It is this remarkable flexibility of application that enabled designers of electronic systems to make electronics the defining technology of the late twentieth century, eclipsing both the mechanical technologies associated with the industrial revolution and the electrical and information Technologies of the so-called second industrial revolution. While many in the post-World War II era once referred to an ‘‘atomic age,’’ it was in fact an era in which daily life was increasingly dominated by electronics.
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